GENUS ICHTHYOCRINUS. 325 



GENUS ICHTHYOCRINUS (Conrad). 

 ICHTHYOCRINUS SUBANGULARIS 



[chthyocrinus subangularis : Hall, Trans, of the Albany Institute, Yol.v. 1863. 



This species is more narrowly turbinate than the /. laevis of the Niagara 

 group in New York, and has the calyx distinctly angular. 



The original of the species occurs at Waldron, associated with well 

 marked Niagara forms ; and a specimen of the same species has been found 

 at Bridgeport, Illinois, in limestone of the age of the Niagara group. 



Possibly a large collection of specimens may show gradations from the 

 rounded and broadly turbinate typical species of the genus, to the narrow 

 and subangular forms of Indiana and Illinois ; but we have no interme- 

 diate forms at the present time. 



GENUS RHODOCRINUS (Miller). 



Subgenus Lyriocrinus (Hall). 

 LYRIOCmNUS SCULPTILIS ( n. s.). 



Body turbinate, rounded at the base, with the arm bases prominent. 

 Basal plates (?) concealed beneath the column attachment. Subradials 

 long, pentagonal. First radials wider than long, heptagonal. Second 

 radials much smaller than the first, somewhat quadrangular in general 

 form, but having the upper lateral angles more or less widely truncated. 

 Third radials broad and short, much smaller than the second, and sup- 

 porting on each of the upper sloping sides two or three supraradials ; 

 giving two arms for each ray. 



The first interradial plates are hexagonal or heptagonal, supporting two 

 or three smaller plates in the second range, with several smaller plates 

 above. 



The arms, as far as known, are two from each ray. The dome is depressed- 

 convex, with a somewhat large proboscis on the anal side [the spaces 

 between the arms being a little greater on that side]. 



The surfaces of the plates are marked by node-like ridges radiating from 

 the centre, and the sutures between the plates are deeply marked and 

 apparently nearly flat in the bottom. 

 The specimens vary from three-fourths of an inch to one inch in height, 



with a diameter of one-half to three-fourths of an inch. They occur as casts 



of the interior, and the characters of the exterior have been derived from 



the natural mould in the limestone. 



Formation and locality. In limestone of the age of the Niagara group 



at Waukesha, Wisconsin. 



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